Answer:
a) Then net force acting on the wagon  30 [N] in a negative direction to the left 
b)Acceleration of the wagon 3 m/s² in a negative direction to the left
Explanation:
The coordinates x and y show the positive direction in x-axis ( to the right) and negative direction to the left. In north-south direction positive y values are to the north and negative values to the south
The free-body diagram shows 4 forces acting
In y-axis:
The weight ( P = m*g =  10 [kg]*9,8 [m/s²] = 98 [N] negative
Normal reaction force  Fn = P = 98 [N]  positive ( surface is frictionless)
∑Fy = 0     P - Fn = 0     P = Fn  = 98 [N]
In x-axis:
Boris pulling force to the right (positive ) 220 [N]
Natasha pulling force to the left ( negative) 250 [N]
∑Fx = m*a
220 [N] - 250 [N]  = 10 Kg * a                      [N] = Kg * m /s²
-30 [kg*m/s²]  = 10 * Kg * a
-30/10  =  - 3  m/s²  = a
Sign (-) means the direction of acceleration vector is to the left (the same direction of the movement )
Then net force acting on the wagon  30 [N] in negative direction to the left
Acceleration of the wagon 3 m/s² in negative direction to the left